Research background: Over the past four years, Dr. Gros has worked as a Department of Veteran Affairs (DVA) Staff Psychologist, providing evidence-based psychotherapies to Veterans with depressive and anxiety disorders and completing related research projects to better understand and improve clinical outcomes in Veterans with these disorders. To date, Dr. Gros has authored 43 peer-reviewed publications and 32 conference presentations at meetings of national and international societies. Dr. Gros has also served as Co- Investigator on two DVA Merit Awards. Immediate and Long-Term Career Goals: Dr. Gros' long-term career goals involve improving the effectiveness, efficiency, dissemination, and implementation of evidence-based psychotherapy for Veterans with depressive and anxiety disorders. Consistent with these long-term goals, Dr. Gros' DVA Career Development Award (CDA) proposes to evaluate a single unified transdiagnostic cognitive behavioral therapy (CBT) in Veterans with depressive/anxiety disorders to improve clinical outcomes and reduce comorbidity as compared to an evidence-based psychotherapy control condition of behavioral activation treatment (BAT). Primary Aims in Career and Mentorship Plan: In order to accomplish these goals, Dr. Gros' CDA also will provide vital trainings in randomized controlled trials (RCTs), including advanced methodology, implementation, statistical evaluation, and grantsmanship. Specialized coursework, scheduled time with mentors, and hands-on trainings will be used to enhance Dr. Gros' background in each of these areas. Relevance of Research Plan: CBT is robustly effective in treating Veterans with severe symptoms of depression and anxiety. However, CBT is underutilized due in large part to the complexity and number of protocols across disorders, as well as extensive training needed to apply them. These limitations have reduced Veterans' access to CBT, resulting in poorer clinical outcomes and quality of life. To address these concerns, world renowned experts in the CBT field have been calling for a new transdiagnostic approach to treatment in order to improve access to care by distilling the existing disorder-specific CBT protocols for emotional problems into an unified CBT protocol for the great majority of depressive/anxiety disorder presentations. Primary Aims in Research Plan: The proposed CDA research aims to: 1) compare the efficacy of transdiagnostic CBT on reducing mental health symptoms and improving quality of life to the BAT control condition, and 2) compare the feasibility and acceptability of the transdiagnostic CBT to the BAT control condition. Participant population: The participants of the proposed study will include 96 DVA patients with depressive/anxiety disorders. General inclusion criteria includes: 1) a principal diagnosis of a depressive/anxiety disorder; and 2) a willingness and competence to provide informed consent for research participation. Procedures to be used: A RCT of the transdiagnostic CBT and BAT control condition will be completed. Participation in the RCT will involve completion of: 1) consent documentation, 2) intake assessment, 3) random assignment to treatment condition, 4) weekly 50 minute appointments of individual psychotherapy for 12-16 weeks, and 5) self-report assessments of symptomatology and quality life at intake, one week post-treatment, and 6-month follow-up. Anticipated Impacts on Veterans Health Care: If successful, this proposed project will lead to reduced symptomatology, comorbidity, and improved quality of life and recovery in DVA patients with depressive/anxiety disorders by eventually improving access to and availability of evidence-based CBT through this new transdiagnostic CBT protocol.